* Handle weights as `distance=` in testing dispatch

* fix `test_intersection`

This change was suggested here:
https://github.com/python-graphblas/graphblas-algorithms/pull/62#issuecomment-1531810715

* Allow multiple graphs for nx._dispatch

A new `graphs` keyword is added. For the case of two graphs named
`G` and `H` as the first to arguments in `foo`, the new spelling is
@nx._dispatch(graphs="G,H")
def foo(G, H, other_arg, **kwargs):
    ...

* Use better default "G" for graphs kwarg

* fix

* Add tests for nx._dispatch decorator

The dispatch functionality is used to delegate graph
computations to a different backend. Because those backends
are not part of NetworkX, testing the dispatching feature
was not originally added, relying instead on the other
backends (e.g. graphblas-algorithms) to verify the dispatch
functionality is working.

This change creates a "loopback" backend where NetworkX dispatches
to itself for the sole purpose of exercising the dispatching
machinery.

In one incarnation, various tests are augmented to use the
LoopbackGraph family and force loopback dispatching to occur
as normal usage would.

A second incarnation forces *all* tests to run in dispatch mode
but use of a different _dispatch decorator. This mode is triggered
for all of pytest, so it must be tested by the CI system specifically.

* Update CI to hopefully run dispatching auto tests

* Formatting

* More formatting fixes

* Better comments explaining dispatching tests

This is a simple follow-up to #6471, and, as in that PR, this fix is short term.
We would like to find a more elegant, robust solution (probably after nx 3.1).

I sometimes forget there are two versions of `_dispatch`, and this PR fixes the
one that gets used when `NETWORKX_GRAPH_CONVERT` environment variable is set.
NetworkX does not yet test `test_override_dispatch`, so it's not easy to add
a test, but it gets used by external backends such as `graphblas_algorithms`.
Ideally, we should test this in NetworkX, which will require calling subprocess
in a test with an environment variable set.

* Ignore weakrefs when testing for memory leak

* Add educational comments about gc and weakrefs

* tweak _dispatch to allow func(G=G) pattern in signature

Co-authored-by: Erik Welch <erik.n.welch@gmail.com>

* lint and fix using ruff

* add flake8-pie lints

* remove useless import alias

* bump version

* bump deps

---------

Co-authored-by: daniel.eades <daniel.eades@hotmail.com>

* Update developer requirements

* Run linter

Minor formatting fixups to get rid of doc build warnings.